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• FFmpeg write silence if there is no data in pipe:0

  15 juillet 2023, par Oleksandr Petrenko

  I have an ffmpeg process that continiously writes PCM data from standard input to an mp3 file. The problem is that sometimes there can be pauses in data being sent to ffmpeg. Pauses may be very large, even up to an hour, but process is never closed. I want to get ffmpeg to write silence to file if there is no data in pipe:0. Is it possible to do only with ffmpeg or I need to implement it on my side ? If it is possible, then how can I do that ?
I tried to use some parameters and filters but I didn't found the thing I need.

  


  I'm new to ffmpeg and working with audio so I will be glad to see any assistance.

  


• CGO : How do you use pointers in Golang to access data from an array in C

  23 avril 2018, par nevernew

  I’m writing an app for the windows platform using FFmpeg and it’s golang wrapper goav, but I’m having trouble understanding how to use the C pointers to gain access to the data array they point to.

  I’m trying to get the data stored in the AVFrame class and use Go to write it to a file, and eventually a texture in OpenGl to make a video player with cool transitions.

  I think understanding how to cast and access the C data will make coding this a lot easier.

  I’ve stripped out all the relevant parts of the C code, the wrapper and my code, shown below :

  C code - libavutil/frame.h

  #include 
  
  
  
  typedef struct AVFrame {
  
  #define AV_NUM_DATA_POINTERS 8
  
      uint8_t *data[AV_NUM_DATA_POINTERS];
  
  }

  Golang goav wrapper - I don’t really know whats going on here with the unsafe.Pointers and casting but it gives me access to the underlying C code

  package avutil
  
  
  
  /*
  
      #cgo pkg-config: libavutil
  
      #include <libavutil></libavutil>frame.h>
  
      #include 
  
  */
  
  import "C"
  
  import (
  
      "unsafe"
  
  )
  
  
  
  type Frame C.struct_AVFrame
  
  
  
  func AvFrameAlloc() *Frame {
  
      return (*Frame)(unsafe.Pointer(C.av_frame_alloc()))
  
  }
  
  
  
  func Data(f *Frame) *uint8 {
  
      return (*uint8)(unsafe.Pointer((*C.uint8_t)(unsafe.Pointer(&amp;f.data))))
  
  }

  My Golang code

  package main
  
  
  
  import "github.com/giorgisio/goav/avutil"
  
  
  
  func main() {
  
      videoFrame := avutil.AvFrameAlloc()
  
  
  
      data := avutil.Data(videoFrame)
  
  
  
      fmt.Println(data) // here i want the values from data[0] to data[7], but how?
  
  }

• Extacting klm data from mp2 stream using c++ and ffmpeg

  19 février 2019, par Douglas

  I have an mp2 stream that has klv metadata. I stored the klv in a file using ffmpeg command line :

  ffmpeg -i input.mpg -map data-re -codec copy -f data output.klv

  I now want to do this in c++. So, I have

  FFMPEG setup …..

  Then the main loop

  // Read frames
  
  while(av_read_frame(pFormatCtx, &packet) >= 0)
  
  {
  
      // Is this a packet from the video stream?
  
      if(packet.stream_index == videoStream)
  
      {
  
          // Decode video frame
  
          avcodec_decode_video2(pCodecCtx, pFrame, &frameFinished, &packet);
  
  
  
          // Did we get a video frame?
  
          if(frameFinished)
  
          {
  
              // Convert the image from its native format to RGB
  
              sws_scale(sws_ctx, (uint8_t const * const *)pFrame->data,
  
                                  pFrame->linesize, 0, pCodecCtx->height,
  
                                  pFrameRGB->data, pFrameRGB->linesize);
  
  
  
              QImage myImage(pFrameRGB->data[0], pCodecCtx->width, pCodecCtx->height, QImage::Format_RGB888);
  
  
  
              QPixmap img(QPixmap::fromImage(myImage.scaled(ui->label->width(),ui->label->height(),Qt::KeepAspectRatio)));
  
  
  
              ui->label->setPixmap(img);
  
              QCoreApplication::processEvents();
  
          }
  
      }
  
      else // klv stream
  
      {
  
          // Decode klv data
  
          qDebug() << packet.buf->size;
  
          for(int i=0; isize; i++)
  
          {
  
              qDebug() << packet.buf->data[i];
  
          }
  
      }

  The resulting klv output is different - I must be doing something wrong processing the packet. The frames are good and I’m viewing it in a qt label - so my ffmpeg setup is working on images but not the klv data. Any ideas ? THANKS